1. Technical Field
The present invention relates to bonding pattern discrimination, and more particularly, to a bonding pattern discrimination method, a bonding pattern discrimination device and a bonding pattern discrimination program for discriminating the inclination of positioning patterns used in bonding.
2. Description of the Related Art
In cases where chips are die-bonded to circuit boards, and in cases where wire bonding that connects wires to bonding leads of circuit boards from the bonding pads of chips disposed on the circuit boards is performed, there may be instances in which the positioning is poor so that the chips are disposed at an inclination. In order to prevent this, the external shapes of the chips themselves or positioning patterns formed on the surfaces of the chips are observed, and this inclination is detected.
Methods in which the edges of the positioning patterns are detected and the inclination is calculated, or methods in which two separated positioning patterns are formed, and the inclination is calculated by defining line segments between these positioning patterns are used to detect the inclination by way of using positioning patterns. In the method of Japanese Patent Application Laid-Open (Kokai) No. S63-56764, pattern matching between a reference-image prepared beforehand and the object-image is performed by successively rotating the reference-image from 0 to 360° for each pattern matching in cases where there is rotation, repeating pattern matching for each angle, and judging the locations and angles that show the best match as a result.
Furthermore, in the method of Japanese Patent No. 2864735, square regions that are to be compared are extracted from object-image signals obtained by imaging, the image signals contained in the extracted square regions are converted into image signals with polar coordinates by way of using the corners of the square regions as the origin, radial-direction patterns for respective specified angles and radial-direction patterns in the reference angles of reference-images prepared beforehand and subjected to a polar coordinate conversion are successively compared, and the comparative angle of the object-image is calculated.
Furthermore, in Japanese Patent Application Laid-Open (Kokai) No. 2002-208010, an approach by way of using a rotation-resistant reference point is disclosed as a means for performing high-precision position detection without performing pattern matching in the rotational direction (which tends to involve an increase in the quantity of calculations) even in cases where the object of comparison is disposed in an attitude that includes positional deviation in the rotational direction. Here, according to Japanese Patent Application Laid-Open (Kokai) No. 2002-208010, the term “rotation-resistant reference point” refers to a point which is such that the error in the position of the object of comparison that is detected in pattern matching of the reference-image and an image of the object of comparison that is obtained by imaging the object of comparison disposed in an attitude that includes positional deviation in the direction of rotation shows a minimum value. Furthermore, in Japanese Patent Application Laid-Open (Kokai) No. 2002-208010, it is indicated that normalized correlation calculations can be used as one method of pattern matching. The following embodiment is shown as a method for calculating the rotation-resistant reference point.
In the first embodiment, the rotation-resistant reference point is calculated as follows. Specifically, with one corner of the reference-image taken as the center, a rotated image that is rotated +Q° is produced, and the coordinates (X1, Y1) of the point showing the best match as a result of pattern matching between this rotated image and the reference-image are determined. Similarly, a rotated image that is rotated −Q° is produced, and the coordinates (X2, Y2) of the point showing the best match as a result of pattern matching between this rotated image and the reference-image are determined. The coordinates (ΔX1, ΔY1) of the rotation-resistant reference point are expressed by the following Equations (1) through (4) by way of using the coordinates (X1, Y1), (X2, Y2) of these two points, the angle Q° and the coordinates (XC1, YC1) of the corner point taken as the center of rotation.AX1=XC1+r cos α  (1)AY1=YC1+r sin α  (2)Here, α=tan−1{(X2−X1)/(Y1−Y2)}  (3)r=√{(X2−X1)2+(Y1−Y2)2}/2 sin Q  (4)
The rotation-resistant reference point determined by this method is the center of the object in cases where the pattern used is the shape of the object. For example, in the case of a circle, the center point of the circle is the rotation-resistant reference point, and in the case of a square, the center point of the square is the rotation-resistant reference point.
The second embodiment is a simpler method for calculating the rotation-resistant reference point. Specifically, a plurality of rotational center points are set within the reference-image. Then, the reference-image is rotated +Q° about each rotational center point. The amounts of matching between the respective rotated images thus obtained and the reference-image are respectively calculated. Then, a rotational center point with a relatively large amount of matching (among the plurality of rotational center points) is taken as the rotation-resistant reference point. In this case, a rotational center point that is set in the vicinity of the center of the pattern used is taken as the rotation-resistant reference point.
It is indicated that the coordinates of points used in bonding can be determined with high precision, without any need to perform pattern matching in the rotational direction, by thus calculating the coordinates of the rotation-resistant reference point, and taking this point as a bonding alignment point, i.e., a bonding positioning point.
In bonding apparatuses or bonding techniques, higher-precision positioning and faster positioning for higher-speed bonding are demanded. The above-described prior art suffers from the following problems in the rapid, high-precision detection of the inclination of positioning patterns used in bonding.
Methods that determine the inclination by edge detection are not suitable for use in cases where considerable edges are not contained in the patterns, and the precision is influenced by the properties of the edges. In methods that determine the inclination of line segments between separated positioning patterns, the visual field magnification drops if an attempt is made to observe both positioning patterns at the same time, so that the precision is poor; furthermore, time is required in order to observe respective positioning patterns in separate visual fields.
In the case of methods in which the reference-image is successively rotated from 0 to 360° when pattern matching is performed, and pattern matching is repeated for the respective angles, the processing time is increased. Furthermore, although a group of reference-images that are successively rotated from 0 to 360° can be prepared beforehand and pattern matching can be performed by way of using these reference-images, the quantity of data is enormous and the processing time is also lengthened.
In the case of methods that use a polar coordinate conversion, the precision is greatly influenced by the manner in which the origin is established. For example, in cases where the positioning pattern has a circular shape, the polar coordinate development can be performed with good reproducibility if the center of the circular shape is taken as the origin of polar coordinate development. However, there is no angle dependence of the developed pattern, so that actual angle detection is impossible. In cases where the positioning pattern is asymmetrical, the conditions of the developed pattern vary according to the placement of the origin of the polar coordinate development; as a result, the precision of angle detection is influenced. In the method disclosed in Japanese Patent No. 2864735, it is proposed that polar coordinate conversions be respectively performed for the four corners of the square regions, and that the inclination-angle be determined based upon these conversions; in this case, however, the processing time increases.
In methods that calculate a rotation-resistant reference point, and take this point as a positioning point of bonding, positions can be determined with high precision, but the inclination-angle of the positioning patterns cannot be determined. In die bonding, however, not only the bonding position of the chip but also the inclination-angle is important, and in wire bonding, not only the position of the positioning pattern but also the inclination-angle of the positioning pattern is important for estimating the positions of the respective bonding pads from positioning pattern information.
Thus, in the prior art, problems remain regarding the rapid, high-precision discrimination of the inclination of positioning patterns used in bonding.